This invention relates generally to an impact printer, and in particular, to an impact dot print head in which printing is effected by striking the tips of printing wires against an ink ribbon.
Impact dot print heads are well known in the art. Generally, in the non-printing state a plunger is held in direct contact with a magnetic core or in contact with a spacer disposed between the plunger and the magnetic core. The plunger is attracted to the core by the magnetic flux of a permanent magnet.
In these impact dot print heads, when the plunger returns to the non-printing (standby) position following a printing operation, the plunger forcibly collides with the core or collides with the spacer which collides with the core. Thus, the plunger and the core are subjected to harsh abrasion and must be replaced frequently. Generally, the materials with good mechanical strength do not have good magnetic qualities. Thus, an impact dot print head including a plunger and a core formed of a high strength material and which resists abrasion would lack good magnetic properties and reduce the efficiency of the magnetic circuit. If the spacer is thickened to absorb the force of the collision, the efficiency of the magnetic circuit also declines. Accordingly, the thickness of the spacer is limited and increasing the space between the core and the plunger is not adequate.
Accordingly, it is desirable to provide an impact dot printer including an impact dot print head in which abrasion of the plunger and core is reduced without sacrificing the efficiency of the magnetic circuit and avoids the disadvantages of the prior art devices described above.